There are many ways, if you are done with the references results, you can use pop-bookmark (Ctrl+,) to back out from the References search. Or you can click on the X on the References tool window to close the top-most item on the stack. Finally, there is an option to not show bitmaps in the margin for references (Tools > Options > Editing > Context Tagging(R) > References > "Show bitmap in margin for each reference"